Fields in which crops are planted rarely have a homogeneous soil composition. Different soil types have a different ability to retain water and nutrients. Also weeds and pests will distribute themselves in a non-uniform fashion across a field. Consequently, if uniform application of fertilizers, pesticides, herbicides, and water is carried out, there will be varied crop yield, pest control, weed control, fungus control, for example. This problem induced the development of customized soil and crop treatment, which has been a very high priority research area in the agricultural industry over the last decade.
Early attempts at customizing soil and crop treatment involved manual plotting of the field, monitoring of soil type and condition, and yield monitoring. Of late, field mapping has become substantially more sophisticated. Computer assisted mapping techniques, together with satellite tracking, are commonly used. However, using field maps to accurately apply chemicals or other materials to the field has proven to be a difficult task.
A general process by which chemicals are typically applied to a field is as follows. A carrier (usually water, or a tank mixed chemical and water) is pumped from a tank out to a boom where nozzles spray the carrier out onto the field. A carrier pump maintains pressure on the system out to the nozzles on the boom so that the nozzles will maintain their correct spray pattern. Additional chemicals are injected into the carrier flow on the low pressure side of the carrier pump. These chemicals are then mixed by the pump on the way to the boom sections. One problem associated with this type of system is that there is a delay between the time that the injected chemicals are injected into the carrier and the time that the carrier/chemical is sprayed from the nozzles on the boom. The injected chemicals must travel a certain distance C from the injection point to the nozzle. While the chemical travels this distance, the vehicle remains in motion. This presents problems when attempting to control application to a specific area. One way to address the problem caused by this delay is to "look ahead" of the application vehicle by the distance d and to control the current chemical injection rate based upon the application rate which is desired at the position corresponding to the distance d ahead of the vehicle's current position, while controlling the carrier rate at the current position.
The need to "look ahead" presents a problem at the field boundary for the injected chemicals. When approaching a boundary, the vehicle will look ahead to the area beyond the boundary and see a zero rate. The controller will therefore turn off the injection pumps a distance d before the boundary. As the vehicle approaches the boundary, the chemical from the carrier pump to the nozzles will spray out, leaving nothing but the carrier solution. When the vehicle then turns around, it will look ahead back into the prescription area of the field, see a non-zero injection rate, and command that rate. However, since the injected chemical has been sprayed out, there will then be a distance d where injected chemical will not be applied while the injected chemical travels between the carrier pump and the nozzles.
A second major problem associated with injection is the recording of data. When spraying chemicals with an injection based application system, the injected chemical is injected into the low pressure side of the pump. The chemical then must travel out to the sprayer tips to be applied. This results in a delay from the time that the injection pump is activated to the time that the chemical is actually applied. The time required for the product to travel from the injection pump to the nozzle tip is also specific to each vehicle type. Additionally, the speed the vehicle travels and the rate commanded for the carrier channel that the injected chemical travels in are not a constant and may vary from field to field. When combined with the injector pumps adjusting their rate as required by prescription and the vehicle look ahead leaving the field boundaries, accurate recording of georeferenced application rates becomes a problem.